More than 11.3 tonnes of rubbish were pulled from Perth's waterways and foreshores in 2011-12.
Figures released by the Swan River Trust show more than 6.3 tonnes of general refuse and five tonnes of timber and rubble were collected from the Swan River in the past 12 months.
Trust officers also retrieved 125 large items, including chairs and tyres, from the Swan Canning Riverpark.
Environment Minister Bill Marmion has described the littering as "inexplicable" and urged the public to stop dropping rubbish in and around Perth's rivers.
"Most disturbing is the mass of plastic bags and fishing line that continues to be found, despite people knowing the terrible impacts these items have on river wildlife from pelicans to dolphins," he said.
Mr Marmion said tyres were the most common large items being dumped, with 48 retrieved in 2011-12, compared to 46 the previous year.
He said nine shopping trolleys were collected, compared to 48 the previous year, as well as 21 chairs, down from 51.
However, the number of vandalised signs thrown in the river, including real estate and street signs, rose from 10 to 19, and the number of drums more than doubled from seven to 16, he said.
The figures come weeks after Keep Australia Beautiful released its national litter index, which indicated West Australians were among the worst with littering in the country, Mr Marmion said.He said the State Government had increased fines for both illegal dumping and littering but the public needed to do its part and stop dumping rubbish in the river.
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